Air/fuel ratio validation for lean burn

ABSTRACT

A multi-cylinder group engine system operable in at least a first mode and a second mode, where in the first mode a first and second cylinder group combust air and fuel, and where in the second mode at least one of the first and second cylinder group combusts air and fuel and the other one of the first and second cylinder group pumps air without injected fuel, the engine system comprising of a first linear exhaust gas sensor disposed in a first exhaust passage to measure air fuel exhausted from the first cylinder group; a first switching type exhaust gas sensor disposed in a second exhaust passage to measure air-fuel exhausted from the second cylinder group; a second linear exhaust gas sensor disposed downstream of a junction between the first exhaust passage and the second exhaust passage; and a controller configured to validate a reading of the first linear exhaust gas sensor during the first mode of engine operation based on a reading of the second linear exhaust gas sensor when a lean air-fuel ratio is commanded.

This application claims priority to U.S. Provisional Application No.60/713,892, filed Sep. 2, 2005, the entire contents of which areincorporated herein by reference.

BACKGROUND

Some engine control strategies monitor operating parameters usingexhaust gas sensors in order to control engine output. For example anengine control strategy may adjust engine torque based on a feedbackair-fuel ratio. Furthermore, some engine control strategiesadvantageously monitor the exhaust gas sensors in order to determinefunctionality.

One approach attempts to monitor air-fuel sensors based on variousparameters includes performing diagnostics on sensors based on thesensor's exposure to different air-fuel ratios and air amounts. See, forexample, U.S. Pat. No. 6,758,185.

However, the inventors herein have recognized that this approach mayhave some disadvantages. For example, when the above approach is appliedto a system with cylinder group specific modes of engine operation andan asymmetric air-fuel sensor configuration in the exhaust, diagnosis ofsensor degradation may have larger errors due to confounded readingsbased on mixed air-fuel measurements as a result of each cylinder groupoperating at a different air-fuel ratio. Furthermore, some sensor typesmay produce more accurate readings in specific air-fuel ratio ranges andmay have different accuracies corresponding to one another. For example,a linear exhaust gas sensor may have more accurate air-fuel ratioreadings in a lean air-fuel ratio range. As another example a switchingtype exhaust gas sensor may have more accurate air-fuel ratio reading atstoichiometry. Therefore, diagnosis of sensor degradation in a systemcontaining various engine modes with different air-fuel ratios anddifferent exhaust gas sensor configurations may have increased errorsdepending on the type of sensor and respective range of measurementaccuracy.

The above issues may be addressed by, in one example, a multi-cylindergroup engine system operable in at least a first mode and a second mode,where in the first mode a first and second cylinder group combust airand fuel, and where in the second mode at least one of the first andsecond cylinder group combusts air and fuel and the other one of thefirst and second cylinder group pumps air without injected fuel, theengine system comprising: a first linear exhaust gas sensor disposed ina first exhaust passage to measure air fuel exhausted from the firstcylinder group; a first switching type exhaust gas sensor disposed in asecond exhaust passage to measure air-fuel exhausted from the secondcylinder group; a second linear exhaust gas sensor disposed downstreamof a junction between the first exhaust passage and the second exhaustpassage; and a controller configured to validate a reading of the firstlinear exhaust gas sensor during the first mode of engine operationbased on a reading of the second linear exhaust gas sensor when a leanair-fuel ratio is commanded.

In this way, air-fuel control readings may be validated in an asymmetricsensor configuration to facilitate accurate engine control throughoutdifferent modes of engine operation. In particular, a linear exhaust gassensor may advantageously be validated based on another linear exhaustgas sensor during lean operation due to the accurate nature of linearexhaust gas sensor measurements in a lean air-fuel ratio range.Furthermore, by validating the readings of the exhaust gas sensors theengine control strategy may reduce the likelihood of inaccurate enginetorque control and estimation, increased emissions and/or reduced fueleconomy due to errors in air-fuel control because of sensor degradation.

BRIEF DESCRIPTION OF THE FIGURES

The above features and advantages will be readily apparent from thefollowing detailed description of example embodiment(s). Further, thesefeatures and advantages will also be apparent from the followingfigures.

FIG. 1 is a schematic depiction of an exemplary embodiment of an engineaccording to the present disclosure.

FIGS. 2A-2C are schematic depictions of different exemplary engine andexhaust system configurations.

FIGS. 3A-3B are flow diagrams of an exemplary embodiment of a method ofestimating maximum torque in an engine.

FIGS. 4A-4B are flow diagrams of an exemplary embodiment of a method ofvalidating air-fuel ratio measurements of UEGO sensors in the exhaustsystem of an engine.

FIG. 5 is a flow diagram of an exemplary embodiment of a method ofverifying fuel injector activity in cylinder groups during various modesof engine operation.

FIG. 6 is a flow diagram of an exemplary embodiment of determiningperformance degradation in various modes of operation of an engine.

FIG. 7 is a schematic diagram of an exemplary embodiment of a fuelinjector activity detection logic circuit.

FIG. 8 is a flow diagram of an alternative exemplary embodiment of amethod of verifying fuel injector cut-out mode and fuel injectoractivity during various modes of engine operation.

FIG. 9 is a schematic diagram of an alternative exemplary embodiment ofa fuel injector cut-out mode activity detection logic circuit.

FIG. 10 is a truth table and graphical representation of the inputs andoutput of the logic circuit of FIG. 9.

DETAILED DESCRIPTION

FIG. 1 shows a schematic diagram of one cylinder of multi-cylinderinternal combustion engine 10. Combustion chamber or cylinder 30 ofengine 10 is shown including combustion chamber walls 32 and piston 36positioned therein and connected to crankshaft 40. A starter motor (notshown) may be coupled to crankshaft 40 via a flywheel (not shown).Cylinder 30 may communicate with intake port 44 and exhaust port 48 viarespective intake valve 52 and exhaust valve 54. Intake valve 52 andexhaust valve 54 may be actuated via intake camshaft 51 and exhaustcamshaft 53. Further, the position of intake camshaft 51 and exhaustcamshaft 53 may be monitored by intake camshaft sensor 55 and exhaustcamshaft sensor 57 respectively. In an exemplary embodiment, intake andexhaust valve control may be provided by signals supplied by controller12 via electric valve actuation (EVA). Additionally intake and exhaustvalve may be controlled by various other mechanical control systemsincluding cam profile switching (CPS), variable displacement engine(VDE), variable cam timing (VCT), variable valve lift (VVL), and/orvariable valve timing (VVT). In some embodiments, valve control strategymay include a combination of two or more of the above mentioned controltechniques. While cylinder 30 is shown having only one intake valve andone exhaust valve, it should be appreciated that in some embodimentscylinder 30 may have two or more intake and/or exhaust valves.

Fuel injector 66 is shown coupled to intake port 44 for deliveringinjected fuel in proportion to the pulse width of signal FPW receivedfrom controller 12 via electronic driver 68. Fuel may be delivered tofuel injector 66 by a fuel system (not shown) including a fuel tank,fuel pumps, and a fuel rail. Engine 10 is described herein withreference to a gasoline burning engine, however it should be appreciatedthat in some embodiments, engine 10 may be configured to utilize avariety of fuels including gasoline, diesel, alcohol, hydrogen, andcombinations thereof.

Intake port 44 is shown communicating with intake manifold 42 viathrottle plate 64. Further, throttle plate 64 may be coupled to electricmotor 62 such that the position of throttle plate 64 may be controlledby controller 12 via electric motor 62. Such a configuration may bereferred to as electronic throttle control (ETC), which may be utilizedduring idle speed control. In an alternative embodiment (not shown), abypass air passageway may be arranged substantially parallel withthrottle plate 64 to control inducted airflow during idle speed controlvia a throttle control valve positioned within the air passageway.

Distributorless ignition system 88 may provide ignition spark tocombustion chamber 30 via spark plug 92 in response to spark advancesignal SA from controller 12. Though spark ignition components areshown, engine 10 (or a portion of cylinders thereof) may not includespark ignition components in some embodiments and/or may be operatedwithout requiring a spark.

Engine 10 may provide torque to a transmission system (not shown) viacrankshaft 40. Crankshaft 40 may be coupled to a torque converter whichis also coupled to a transmission via a turbine shaft. Torque convertermay include a bypass, or lock-up clutch. The lock-up clutch may beactuated electrically, hydraulically, or electro-hydraulically, forexample. The transmission may comprise an electronically controlledtransmission with a plurality of selectable discrete gear ratios.Alternatively, in some embodiments, the transmission system may beconfigured as a continuously variable transmission (CVT), or a manualtransmission.

Exhaust gas sensor 126 is shown coupled to exhaust port 48 upstream ofcatalytic converter 70. It should be noted that sensor 126 maycorrespond to a plurality of various different sensors and catalyticconverter 70 may correspond to a plurality of various emissions devicespositioned in the exhaust, depending on the exhaust configuration(described in detail below with regard to FIGS. 2A-2C). Sensor 126 maybe any of many know sensors for providing an indication of exhaust gasair/fuel ratio such as an exhaust gas oxygen (EGO) sensor, linear oxygensensor, an UEGO, a two-state oxygen sensor, a HEGO, or an HC or COsensor. For example, a higher voltage state of signal EGO indicates thatexhaust gases may be rich of stoichiometry and a lower voltage state ofsignal EGO indicates that exhaust gases may be lean of stoichiometry.Further, signal EGO may be used during air/fuel control in order toestimate and validate various aspects of a desired engine control modeas will be described in greater detain below.

Controller 12 is schematically shown in FIG. 1 as a microcomputer,including microprocessor unit (CPU) 102, input/output ports 104, anelectronic storage medium, (ROM) 106, random access memory (RAM) 108,keep alive memory (KAM) 110, and a data bus. Controller 12 is shownreceiving various signals from sensors coupled to engine 10, in additionto those signals previously discussed, including measurement of inductedmass air flow (MAF) from mass air flow sensor 120 coupled to intakemanifold 42; engine coolant temperature (ECT) from temperature sensor112 coupled to cooling sleeve 114; a profile ignition pickup signal(PIP) from Hall effect sensor 118 coupled to crankshaft 40; and throttleposition TP from throttle position sensor in electronic motor 64; andabsolute Manifold Pressure Signal MAP from sensor 122. A pedal positionindication (PP) may be determined by a pedal position sensor 134 thatsenses the angle of pedal 130 according to driver input 132. Enginespeed signal RPM may be generated by controller 12 from signal PIP andmanifold pressure signal MAP from a manifold pressure sensor provides anindication of vacuum, or pressure, in the intake manifold. Controller 12may be configured to cause combustion chamber 30 to operate in variousmodes of operation including homogeneous or stratified spark ignition orcompression ignition modes, for example. Controller 12 may control theamount of fuel delivered by fuel injector 66 so that the air/fuelmixture in cylinder 30 may be selected to be at stoichiometry, a valuerich of stoichiometry or a value lean of stoichiometry. In someembodiments, controller 12 may control the amount of fuel vapors purgedinto the intake port via a fuel vapor purge valve (not shown)communicatively coupled thereto. Further, in some embodiments, engine 10may include an exhaust gas recirculation (EGR) system that routes adesired portion of exhaust gas from exhaust port 48 to intake port 44via an EGR valve (not shown). Alternatively, a portion of combustiongases may be retained in the combustion chambers by controlling exhaustvalve timing.

As described above, FIG. 1 merely shows one exemplary cylinder of amulti-cylinder engine, and that each cylinder has its own set ofintake/exhaust valves, fuel injectors, spark plugs, etc. Furthermore,although the above described engine is shown with a port injectionconfiguration, it should be appreciated that an engine may be configuredto inject fuel directly into the cylinders without parting from thescope of this disclosure.

FIGS. 2A-2C show exemplary multi-group engine configurations (such as2-bank engines, etc.) with Y-pipe exhaust, and/or an asymmetric sensorconfiguration. Note that these Figures are purely exemplary and othermulti-group engine configurations also may be used. It should beappreciated that a cylinder group may include one or more cylinders.Further, note that while numerous sensors are shown throughout theexhaust system, in some embodiments a subset of these sensors may beused.

Referring now to FIG. 2A, an exemplary asymmetric exhaust sensorconfiguration is described using a V-8 engine. The asymmetricconfiguration may be beneficial for detection of different operatingcondition throughout operation of different engine modes. Cylinders of afirst combustion chamber group (which are shown as a bank, although thegroup may include cylinders from multiple banks, or may include a subsetof cylinder in a bank) 210 may be coupled to first catalytic converter220, while cylinders of a second combustion group 210 (which is alsoshown as a bank, but as noted above is not necessarily limited to abank) may be coupled to second catalytic converter 222. Linear exhaustgas sensor 230 may be disposed between engine group 210 and firstcatalyst 220. In some embodiments sensor 230 may be a universal exhaustgas oxygen (UEGO) sensor. Further, switching type exhaust gas sensor 232may be disposed downstream of first catalyst 220. In some embodimentssensor 232 may be a heated exhaust gas oxygen (HEGO) sensor. Switchingtype exhaust gas sensor 234 may be disposed between engine group 212 andsecond catalyst 222. Further, switching type exhaust gas sensor 236 maybe disposed downstream of second catalyst 222. In some embodimentssensors 234 and 236 may be HEGO sensors. Exhaust gas exiting from firstcatalyst 220 and second catalyst 222 merge in a Y-pipe configurationbefore entering downstream under body catalyst 224. In some embodimentsdownstream catalyst 224 may be a lean NOx trap. Temperature sensor 238may be disposed in underbody catalyst 224, while a combined NOx-UEGOsensor 240 may be disposed downstream of underbody catalyst 224.

Note that a linear exhaust gas sensor (more specifically a UEGO sensor)may provide a substantially linear indication of exhaust air-fuel ratioacross a range of air-fuel ratios from at least 12:1 to 18:1, or 11:1 to20:1, or various other ranges and subranges. The substantially linearrelationship between the sensor output voltage and exhaust gas oxygenconcentration allows the sensor to operate across a wide range ofair-fuel ratios, and therefore can provide advantageous information whenoperating away from stoichiometry.

Further note that a switching type or non linear exhaust gas sensor(more specifically a HEGO sensor) may provide a high gain betweenmeasured oxygen concentration and voltage output. That is, a nonlinearsensor may produce an output that is close to being a step change involtage at stoichiometry. Hence, the switching type exhaust gas sensormay provide an accurate indication of the stoichiometric point based onthe voltage step output.

In some embodiments, various sensors may be integrated into thecatalysts while other sensors may be placed upstream or downstream ofthe catalyst. For example, sensor 240 may be integrated into underbodycatalyst 224 or sensor 238 may be placed upstream of underbody catalyst224. Further, in some embodiments sensors may be disposed between bricksin a multi-brick catalyst, such as sensor 240.

Also, sensors 230-240 may be sensors of various types. For example, thesensors may be any of many example sensors for providing an indicationof exhaust gas air/fuel ratio such as a linear oxygen sensor forproviding indication of air-fuel ratio across a broad range, a switchingtype exhaust gas oxygen sensors that provide a switch in sensor outputat the stoichiometric point, a UEGO, a two-state oxygen sensor, an EGO,a HEGO, or an HC or CO sensor. Furthermore, in some embodiments, mixedsensor types may be used, for example, a UEGO sensor may also have NOxdetection capabilities.

In some embodiments first catalyst 220 and second catalyst 222 may bethree way catalysts that retain oxidants when operating lean and releaseand reduce the retained oxidants when operating rich. Additionally,underbody catalyst 224 may be configured to operate as a lean NOx trapwhich may reduce residual oxidants that flow downstream. Further, theillustrated catalysts may represent multiple bricks, and/or mayrepresent several separate emission control devices. Note that in someembodiment various other emission control devices may be used.

The above described configuration may be considered asymmetric due tothe fact that two or more engine banks or groups may be monitored by atleast one different type of sensor. In this particular embodiment, feedgas from first bank or cylinder group 210 may be monitored by linearexhaust gas sensor 230, while feed gas from second engine bank orcylinder group 212 may be monitored by a switching type exhaust gassensor 234. Furthermore, note that in some embodiments the linearexhaust gas sensor and the switching type exhaust gas sensor may beconfigured such that the sensors may be disposed in exhaust flows of theengine banks or groups opposite of what is shown in FIGS. 2A-2C. In someembodiments, the asymmetric configuration may be applied to variousother cylinder groupings and/or exhaust system configurations. Forexample, in an asymmetric configuration sensors may be located inpositions downstream of catalysts, or one sensor may be upstream andanother downstream.

Also, while FIG. 2A shows a V-8 engine, various other numbers ofcylinders may be used. For example, an I-4 engine may be used, wherethere are two groups of two cylinders leading to a common exhaust pathwith upstream and downstream emission control devices.

Referring now to FIG. 2B, a system similar to that in FIG. 2A is shown,however a V-6 type engine is shown, rather than a V-8 engine.

Referring now to FIG. 2C, a system similar to that in FIG. 2A is shown,however an inline type engine (I-6) is shown, rather than a V-8 engine.

As described below, such asymmetric configurations may be used toadvantage during various modes of operation, such as, for example,stoichiometric operation, lean burn operation, operation ofdecontamination cycles, in particular, desulfation (DeSOx) mode, partialcylinder fuel cut-out mode, as well as various other modes of operation.

For example, the engine may operate at stoichiometry, namely one or more(e.g. both) engine banks or cylinder groups may operate with an air-fuelratio about stoichiometry. Furthermore, the engine may operate leanwherein both engine banks or cylinder groups may operate with anair-fuel ratio lean of stoichiometry in order to increase fuel economy.

Additionally, during decontamination cycles, such as desulfation (DeSOx)mode, for example, first engine group 210 may operate with an air-fuelratio that is rich and second engine group 212 may operate with anair-fuel ratio that is lean. In this way, the mixed exhaust from the twoengine banks may be substantially stoichiometric downstream and generateexothermic heat. During DeSOx mode the engine groups further mayalternate between rich and lean operation within each cycle in order toreduce particulate buildup in the catalysts.

Furthermore, during lean burn partial cylinder fuel injector cut-outmode a first group of cylinders may operate lean, and a second group ofcylinders may induct gasses without injected fuel. This mode of engineoperation may increase fuel economy while also increasing engine outputefficiency. Alternatively, in a stoichiometric partial cylinder fuelinjector cut-out mode, a first group of cylinders may operate aboutstoichiometry, and a second group of cylinders may induct gases withoutinjected fuel. In still another example, partial cylinder fuel injectorand cylinder valve deactivation may be used, where the cylinder valvesand fuel injectors may be deactivated. This mode of operation mayprovide engine output characteristic similar to that of a variabledisplacement engine due to the fact that the cylinders with fuel cut-outalso have valve deactivation in order to maintain stoichiometric outputby the active cylinders so that the exhaust may be treated in the threeway catalysts.

Furthermore, in some embodiments a controller may be configured tooperate the engine in a mode, where both the first and second cylindergroups pump air without injecting fuel. This mode of operation may beused for example, during vehicle deceleration to further improve fueleconomy.

It should be appreciated that during fuel injector cut-out modescylinders designated for fuel cut-out may be grouped by engine group orbank. Alternatively, in some embodiments a particular cylinder groupingmay include cylinders in both engine banks. Further, fuel cut-out may belimited to individual cylinders or groups of cylinders. Cylindergroupings may be designated according to an engine control strategy.Such a strategy may designate an engine bank or cylinder group for fuelinjector cut-out based on detection of various operating conditions. Forexample, fuel injector cut-out mode may switch between engine banks orcylinder groups to maintain even wear on cylinders in each engine bankor cylinder group.

Note that the above engine modes are exemplary. Further, the abovedescribed engine operations may be employed in combination with otheroperating modes or may include variations based on different operatingparameters. For example, each of the above modes may include furthervariations based on, for example, cam timing, valve lift, throttleposition, etc.

Additional details of control routines are included below which may beused with various engine configurations, such as those described inFIGS. 1 and 2A-2C. As will be appreciated by one of ordinary skill inthe art, the specific routines described below in the flowcharts mayrepresent one or more of any number of processing strategies such asevent-driven, interrupt-driven, multi-tasking, multi-threading, and thelike. As such, various acts or functions illustrated may be performed inthe sequence illustrated, in parallel, or in some cases omitted.Likewise, the order of processing is not necessarily required to achievethe features and advantages of the example embodiments of the inventiondescribed herein, but is provided for ease of illustration anddescription. Although not explicitly illustrated, one of ordinary skillin the art will recognize that one or more of the illustrated acts orfunctions may be repeatedly performed depending on the particularstrategy being used. Further, these figures may graphically representcode to be programmed into the computer readable storage medium incontroller 12.

FIGS. 3A-3B show flow diagrams depicting a method of estimating maximumtorque produced by an engine during various modes of operation, whereinthe engine exhaust may be configured with an asymmetric exhaust sensorconfiguration. Specifically, the example approaches described herein maybe used to estimate torque in a robust manner such that issuesassociated with inaccurate torque estimations may be addressed. Forexample, in the case of a continuously variable transmission, if theactual torque is higher than the estimated torque, excessive wear and/ordamage to the transmission may occur over time due to insufficientclutch/band pressure. However, if the estimated torque is less than theactual torque the clutch/band pressure may be set higher than optimalresulting in reduced drivability and fuel economy. The torque estimationprocess described in FIGS. 3A-3B may be used to overcome some of theseissues resulting in a more robust control strategy.

Now referring to FIG. 3A, one example routine of torque estimationbegins at 310, where the engine bank or cylinder group specific air-fuelratios are determined. While this routine describes a bank specificapproach, various types of cylinder groupings may be used, as notedherein with regard to FIG. 2. As shown in FIG. 3B, the determination of310 varies according to the detected mode of operation. If it isdetermined that the engine is operating in a lean bum mode, the routinemoves to 312, where the air-fuel ratio measured by the feedgas UEGOsensor may be validated via an air-fuel ratio validation routine(described in more detail below with regard to FIGS. 4A-4B). If theair-fuel ratio measurement from the feedgas UEGO sensor is validated, itmay be assumed that each engine bank or cylinder group is operatingunder the same or similar lean conditions. Thus, the air-fuel ratiodetermination can be assumed to be the same for each engine bank orcylinder group. Accordingly, the air-fuel ratio of each engine bank orcylinder group may be determined by comparing the commanded (desired)air-fuel ratio for each engine bank or cylinder group from the enginecontroller to the actual air-fuel ratio measured by the feedgas UEGOsensor. The smaller (richer) of the two air-fuel ratios may bedetermined to be the air-fuel ratio used for the maximum torqueestimation. If the determined air-fuel ratio is rich beyond a desiredtorque output value, the air-fuel ratio may be clipped to the desiredtorque output value.

In the case where the feedgas UEGO sensor validation is unsuccessful,the commanded air-fuel ratio may be used for the maximum torqueestimation. Furthermore, if the commanded air-fuel ratio is rich beyonda desired torque output value, the air-fuel ratio may be clipped to thedesired torque output value.

If it is determined that the engine is operating in a DeSOx mode, theroutine moves to 314. As discussed above, during DeSOx mode a firstengine bank or cylinder group may operate lean and a second engine bankor cylinder group may operate rich. The air-fuel ratio of the enginebank or cylinder group operating lean may be determined by comparing thecommanded air-fuel ratio from the engine controller to the actualair-fuel ratio measured by the feedgas UEGO sensor. The smaller (richer)of the two air-fuel ratios may be determined to be the air-fuel ratioused for the maximum torque estimation. If the determined air-fuel ratiois rich beyond a desired torque output value, the air-fuel ratio may beclipped to the desired torque output value.

Furthermore, the air-fuel ratio of the engine bank or cylinder groupoperating rich may be assumed to be operating at stoichiometry orslightly rich for a desired maximum output value.

If it is determined that the engine is operating in a lean bum injectorcut-out mode, the routine moves to 316. In this engine operation mode,the air-fuel ratio determination may be made for the active engine bankor cylinder group. When the engine bank or cylinder group upstream ofthe feedgas UEGO sensor is active, the air-fuel ratio may be determinedby comparing the commanded air-fuel ratio from the engine controller tothe actual air-fuel ratio measured by the feedgas UEGO sensor. Thesmaller (richer) of the two air-fuel ratios may be determined to be theair-fuel ratio used for the maximum torque estimation. If the determinedair-fuel ratio is rich beyond a desired torque output value, theair-fuel ratio may be clipped to the desired torque output value. Insome instances the desired output value may be a maximum torque value.

Otherwise, if the active engine bank or cylinder group is on the otherbranch of the Y-pipe exhaust (non UEGO sensor branch) the air-fuel ratiomay be determined to be the commanded air-fuel ratio.

It should be appreciated that in some embodiments the air-fuel ratio foreach engine bank or cylinder group may be determined only using thecommanded air-fuel ratio. For example, in some V-8 engine configurationscylinders may be grouped such that a cylinder group may produce exhaustdown both pipes of a Y-pipe exhaust configuration. In such aconfiguration not all exhaust from the active cylinder group may travelpast the feedgas UEGO sensor making the measurements from the feedgasUEGO sensor erroneous with regard to accurately determining the cylindergroup's air-fuel ratio. In this example, when the engine is in lean bumfuel injector cut-out mode, the air-fuel ratio for each engine bank orcylinder group is assumed to be the commanded air-fuel ratio.

If it is determined that the engine is operating in a stoichiometricinjector cut-out mode, the routine moves to 318. In this engineoperating mode, the air-fuel ratio determination is made for the activeengine bank or cylinder group, and the air-fuel ratio of the activeengine bank or cylinder group may be assumed to be stoichiometry orslightly rich of stoichiometry for the estimate of maximum torque outputvalue.

If it is determined that the both engine banks or cylinder groups areoperating at stoichiometry, the routine moves to 320. At 320, theair-fuel ratio of both engine banks or cylinder groups can be assumed tobe stoichiometry or slightly rich of stoichiometry for the estimate ofmaximum torque output value.

It should be appreciated that in some embodiments the commanded air-fuelratio term used in the above described engine bank or cylinder groupspecific air-fuel ratio determination may further include a long termcorrection term which may take into account engine component degradationand other suitable correction factors.

After the engine bank or cylinder group specific air-fuel ratios aredetermined, the routine moves to 330 where the spark delta of eachengine bank or cylinder group may be calculated. This calculation may beperformed in different ways. In one example, a spark delta figure may beretrieved from a lookup table mapped to the minimum spark timing forbest torque (MBT) output across the operating range of the engine, basedon such conditions as coolant temperature, humidity, air temperature,and/or various others.

Next, the routine calculates the torque ratio of each engine bank orcylinder group at 340 using the previously determined engine bank orcylinder group specific air-fuel ratios and spark delta. Further at 350,the routine calculates the torque ratio of the active engine bank if theengine is operating in a fuel injector cut-out mode. This calculationmay also be supported by verification of the fuel injector activity by afuel injector activity verification routine (discussed in more detailbelow with regard to FIGS. 5A-5B).

Continuing on, the routine calculates the total torque ratio of eachengine bank at 360 using the determined air-fuel ratios, spark delta,and fuel injector activity verification information. In some embodimentsa percent methanol figure may also be taken into consideration toaccount for the combustibility and/or energy density of the fuel.

Next at 370, routine 300 calculates the combined engine bank torqueratio while taking into consideration the weighted torque contributionof the active cylinders in each engine bank. Specifically, the combinedtorque ratio of the engine (tr_act_cond) may be calculated by adding theactual torque (tr_act_cond_a[0]) produced by cylinders in a fist enginebank (bank [0]) multiplied by the number of active cylinder in that bank(numcyl_A[0]) to the actual torque (tr_act_cond_a[1]) produced bycylinders in a second engine bank (bank [1]) multiplied by the number ofactive cylinders in that engine bank (numcyl_A[1]).

Further at 380, the routine calculates the combustion/indicated torque.Specifically, the combustion/indicated torque (tqe_ind_act) may becalculated by multiplying the previously calculated combined torqueratio of the engine (tr_act_cond) with the indicated torque (tqe_ind),where the indicated torque is the MBT torque output at stoichiometry.

Finally at 390, the routine calculates the brake (net) torque.Specifically, the brake torque (tqe_brk) equals the combustion/indicatedtorque (tqe_ind_act) minus the total torque loss (tqe_loss). The totaltorque loss may be the sum of the losses due to friction, pumpinglosses, parasitic losses associated with a front engine accessory drive(FEAD), and any other suitable loss determinant. Accordingly, torqueestimation routine 300 may be repeated numerous times throughout engineoperation in order to provide a robust engine control strategy.

In this way, a robust maximum engine torque estimation may be made foran engine control system that includes different modes of engineoperation. Furthermore, the robust torque estimation may facilitateengine output according to driver demand without causing adverse affectssuch as for example, reduced fuel economy and lowered drivability. Theabove estimated torque may be used for various operations, such ascontrolling/adjusting a ratio of a stepped or continuously variabletransmission, controlling/adjusting transmission clutch pressures,monitoring engine torque production versus driver demand, adjustingengine actuators such as a throttle position or spark timing, andvarious others.

Furthermore, in some embodiments an additional feedgas linear exhaustgas sensor may be disposed in the exhaust passage coupled to the secondcylinder group, so that a linear exhaust gas sensor may be used todetect the air-fuel ratio of each of the first and second cylindergroups. In such a configuration the smaller (richer) air-fuel ratio ofthe two feedgas linear exhaust gas sensors may be used for the maximumtorque estimation. Note that in some embodiments additional linearexhaust gas sensors may be disposed in the exhaust system downstream ofthe feedgas linear exhaust gas sensors for added redundancy andconfirmation of measured air-fuel ratios.

In an exemplary embodiment, electronic engine controller 12 may furtherinclude an on-board diagnostic (OBD) system (not shown). The OBD systemmay detect operating component degradation through various diagnosticroutines. In some instances, if a routine detects performancedegradation, the routine may set a fault (or condition) flag and maytrigger a diagnostic trouble code (alternatively referred to as aservice code) in the electronic engine controller. As another example,if a routine detects performance degradation, one or more modes ofoperation may become restricted or disabled. Many routines within theon-board diagnostics system may detect emission related degradation in arange of operating conditions of the engine.

One embodiment advantageously implements a routine to monitor air-fuelmeasurements from a feedgas UEGO sensor in order to prevent air-fuelcontrol operation based on errors in the feedgas UEGO sensor. Exemplaryair-fuel validation routine 400 may be used to validate a feedgas UEGOsensor measurement in an asymmetric exhaust sensor configuration basedon a downstream UEGO sensor measurement. Specifically, the routinevalidates the feedgas UEGO senor measurement by comparing it to thetailpipe UEGO sensor measurement, while also taking into considerationmode of engine operation, transportation delay times, catalyst impactand other noise factors.

Now referring to FIG. 4A, routine 400 begins by buffering feedgas UEGOmeasurements taken over a period of three seconds into memory in theengine controller at 410. Although the routine buffers feedgas UEGOsensor measurements over a period of three seconds, it should beappreciated that any suitable period of time or number of events, suchas crank angles, may be buffered so long as it is sufficient to coverthe maximum exhaust transportation time from the feedgas to tailpipeUEGO locations.

Next at 412, routine 400 checks the entry conditions for the air-fuelvalidation routine. Specifically, the routine confirms that both enginebanks are operating in a lean bum mode, that all fuel injectors areactive, and that no misfires are taking place. These checks areperformed because certain modes of operation and engine conditions maycause the UEGO sensors' readings to not accurately represent theair-fuel ratio of the engine.

For example, in DeSOx mode a lean air-fuel ratio exhausted from oneengine bank may be read by the feedgas UEGO sensor, and a rich air-fuelratio may be exhausted from the other engine bank. Further, the air-fuelratios may combine downstream to become approximately stoichiometricbefore being read by the tailpipe UEGO sensor. In this case, the feedgasUEGO sensor on one engine bank measures lean, however the rich exhaustfrom the other engine bank causes the measurement of the air-fuel ratioread by the tailpipe UEGO sensor to be skewed. As another example, whenfuel injectors are deactivated in an engine bank but the valves are leftactive, the air flowing through these cylinders into the exhaust mayalso skew the tailpipe UEGO reading. Furthermore, cylinder misfires mayskew UEGO sensor measurements by producing inconsistent air-fuel ratios.Thus, air-fuel measurements may be validated when both engine banksoperate in a lean burn mode, all fuel injectors are active, and nocylinder misfires are taking place.

If conditions in 412 are not met, the routine the routine ends.Otherwise, if the conditions in 412 are met, the routine transitions tostep 414.

Next at 414, routine 400 increments a timer to measure the amount oftime for the exhaust gas to travel from the feedgas UEGO sensordownstream and saturate the catalysts causing an oxygen breakthrough tooccur. While this example uses time, various other durations may beused, such as a number of engine cycles, or other such non-time basedduration.

At 416, routine 400 determines if the measured time is greater than anexpected breakthrough time or if the exhaust sensor system detects anoxygen breakthrough. The expected breakthrough time may be calculatedusing a function based on the measured air mass (fn(AM)) of the exhaust.If not enough time has elapsed since the entry conditions weredetermined to be suitable for air-fuel validation and the oxygenbreakthrough in the catalysts has not been detected, routine 400 ends.However, if enough time has elapsed or an oxygen breakthrough hasoccurred routine 400 moves to 418.

At 418, routine 400 calculates the expected transportation delay timefor the exhaust to travel from the feedgas UEGO sensor to the tailpipeUEGO sensor. The expected transportation delay time may be calculatedusing a function based on the measured air mass and air speed(FN(AM,N)). It should be noted that a variety of other parameters couldalso be used to determine the transportation delay time.

Next at 420, routine 400 looks up the buffered feedgas UEGO measurements(see 410) based on the expected transportation delay. Specifically, theexpected delay time is subtracted from the present time and the feedgasUEGO reading taken at that time may be used. Additionally, routine 400looks up buffered feedgas UEGO measurements taken at a time before andat a time after the measurement taken at the expected time delay. Themeasurement times may be shifted a distance from the expected time delaymeasurement according to a calibratible time shift based on variousoperational conditions, for example, component degradation, and othersuitable control strategies.

At 422, routine 400 determines a maximum value (MAX) and a minimum value(MIN) of the three feedgas UEGO measurements.

Next at 424, routine 400 shifts the minimum and maximum values toaccount for a known signal measurement shift between the feedgas UEGOsensor reading and the tailpipe UEGO sensor reading. Specifically, atailpipe UEGO sensor measurement in many cases reads lower than afeedgas UEGO sensor measurement. This shift may be based on the dynamicsof the exhaust system and the interaction of the exhaust flow with thecatalysts.

Continuing on at 426, routine 400 compares the maximum and the minimumvalues to the tailpipe UEGO sensor measurement of the air-fuel ratio.These comparisons determine if the tailpipe UEGO sensor is operatingwithin the expected window (or range). In some embodiments, the maximumand minimum values further may be shifted by calibratible limits thatmay be used to account for the tolerances of the exhaust sensor system.If it is determined that the tailpipe UEGO sensor measurement is betweenthe maximum and minimum value +/− a calibratible limit, it may beassumed that the tailpipe UEGO sensor is operating as expected, androutine 400 decrements a fault counter at 428 and the routine ends.

Otherwise, if it is determined that the tailpipe UEGO sensor measurementis outside of the maximum and minimum values then the fault counter isincremented at 430.

Next at 432, routine 400 compares the fault counter to a calibratiblethreshold to determine if degradation has occurred in the UEGO sensors.If the fault counter is greater than the calibratible threshold then itmay be assumed that degradation has occurred and an air-fuel validationcondition flag may be set at 434. Note that setting of an air-fuelvalidation flag may result in engine control strategy reconfigurationwhich may include default engine operations (discussed in more detailbelow with reference to FIG. 6). Otherwise the fault counter is notgreater than the calibratible limit and the routine ends. Accordingly,air-fuel validation routine 400 may be repeated numerous timesthroughout engine operation in order to provide a robust engine controlstrategy.

Note that according to the above routine, the feedgas linear exhaust gassensor readings may not be verified based on the downstream linearexhaust gas sensor readings under various operating conditions and invarious modes of engine operation. In particular, if the entryconditions for the verification routine are not met, the engineoperating conditions are likely to produce confounded readings in thedownstream linear exhaust gas sensor due to a combination of differentair-fuel ratios produced by each cylinder group which mix as the exhaustgas travels through the exhaust system. Additionally, engine misfiresand/or no fuel injection may skew the detected air-fuel ratio to beleaner than during full cylinder group combustion.

Furthermore, the above routine advantageously checks for suitable entryconditions including lean operation because linear exhaust gas sensorsmay have more accurate air-fuel ratio readings in a lean air-fuel ratiorange. By performing linear exhaust gas sensor verification anddiagnosis of degradation in an asymmetric exhaust configuration duringlean operation errors related to sensor type and respective range ofmeasurement accuracy may be reduced.

In this way, a feedgas UEGO sensor in an asymmetric exhaust sensorsystem may be validated in order to prevent unexpected engine output andmaintain a functional engine control strategy.

One exemplary embodiment advantageously implements a fuel injectoractivity verification routine as part of a robust engine controlstrategy. Referring to FIG. 5, exemplary fuel injector activityverification routine 500 is shown. Specifically, routine 500 verifiesthat fuel injectors are, in fact, deactivated when the associatedcylinder are commanded to be cut-out and/or disabled as part of theengine control strategy. For example, in some powertrain controlstrategies it may be desirable from a fuel economy standpoint to disablea portion of the cylinder fuel injection and increase the air load ofthe remaining active cylinders in order to maintain a desired enginetorque. During such a mode of operation if the cylinders are commandedto be deactivated but the fuel injectors remain active and the air loadis increased, then an increased amount of torque may be produced. Theverification routine described in FIG. 5 may be used to overcome some ofthese issues resulting in a more robust control strategy. Fuel injectoractivity verification routine 500 begins at 510 where the fuel injectionactivity signals may be read to determine the actual fuel injectoractivity for each of the cylinder groups. In some embodiments, fuelinjection activity may be communicated to the electronic enginecontroller via logic circuitry.

Referring now to FIG. 7, an exemplary sense fuel injector activitycircuit 700 is shown. In this example cylinder group 210 and cylindergroup 212 each include four cylinders (not shown) and four fuelinjectors, respectively. However, note that the number of cylindersand/or fuel injectors may vary in each cylinder group. Furthermore, eachfuel injector may be connected to a sense injector line that shows thefuel injection activity for each cylinder. The sense injector linesassociated with cylinder group 210 may be inputs into “AND” logic gate702 and the sense injector lines associated with cylinder group 212 maybe inputs into “AND” logic gate 704. The outputs of “AND” logic gates702 and 704 may provide signals showing whether or not there is fuelinjector activity in either of the cylinder groups. The outputs of “AND”logic gates 702 and 704 further may be inputs into the electronic enginecontroller 12, which may indicate whether or not there is any fuelinjector activity in a specific group of cylinders.

It should be appreciated that the above described Boolean logic circuitis exemplary. Note that the exemplary circuit may be included as part ofa larger logic circuit. Alternatively, other logic operations may beperformed to indicate fuel injector activity from the sense injectorlines. In some embodiments, the logic circuit may include feedback froma commanded fuel injection signal. Although the Boolean logic circuit isschematically illustrated with discrete logic gates, it should beappreciated that in some embodiments, logical operations may beperformed using customizable integrated circuits, a programmablemicrocontroller and/or the engine controller.

Continuing at 520, the routine determines if the controller hascommanded fuel injector activity for any of the specific cylindergroups. For example, if at least one fuel injector in the group has beencommanded on, the group of cylinders may be considered to be activelyinjecting fuel. If no fuel injectors are commanded on, the group ofcylinders may be considered to be inactive.

Next at step 530, the routine checks if the actual fuel injectoractivity for the first cylinder group from step 510 agrees with thecommanded injector activity for the first cylinder group determined instep 520. If the commanded activity agrees with the actual activity, theroutine moves on to step 540. At 540, the routine decrements a faultcounter and transitions to step 560. If at step 530 the commandedactivity does not agree with the actual activity, the routine moves tostep 550. At 550, the routine increments a fault (or condition) counterand then checks the fault (or condition) counter to a calibratiblethreshold at step 552. If the fault (or condition) counter exceeds thisthreshold, the routine sets a condition flag and transitions to step560. The condition flag may be used by other routines to change the modeof operation as will be discussed in further detail below (see steps 644and 652 of FIG. 6). If the fault (or condition) counter does exceed thecalibratible threshold, the routine transitions to step 560.

Next at step 560, the routine checks if the actual fuel injectoractivity for the second group from step 510 agrees with the commandedinjector activity for the second group determined in step 520. If thecommanded activity agrees with the actual activity, the routine moves tostep 570. At 570, the routine decrements a fault counter and exits theroutine. If at step 560 the commanded activity does not agree with theactual activity, the routine moves to step 580. At 580, the routineincrements a fault (or condition) counter and then checks the fault (orcondition) counter to a calibratible threshold at step 582. If the faultcounter exceeds this threshold, the routine sets a condition flag andexits the routine. The condition flag may be used by other routines tochange the mode of operation as will be discussed in further detailbelow (see steps 644 and 652 of FIG. 6). If the fault (or condition)counter does exceed the calibratible threshold, the routine ends. Thefuel injector activity verification routine 500 may be repeated numeroustimes throughout engine operation in order to provide a robust enginecontrol strategy.

In an alternative embodiment, fuel injection activity may becommunicated to the electronic engine controller through a single lineusing logic circuitry. Specifically, logic circuitry may be used todetermine if a fuel-injector cut-out mode is active or inactive.

Referring to FIG. 8, Fuel injector activity verification routine 800begins at 810 where the fuel injection signal may be read off of thesense injector line to determine the fuel injector activity for theengine groups. Next, at 820 it may be determined if the engine is infuel injector cut-out mode.

In some embodiments, the fuel injector cut-out mode determination may beperformed using a Boolean logic circuit. Referring now to FIG. 9, anexemplary fuel injector cut-out determination circuit 900 is shown. Inthis example cylinder group 210 and cylinder group 212 each include fourcylinders (not shown) and four fuel injectors, respectively. However,note that the number of cylinders and/or fuel injectors may vary in eachcylinder group. Furthermore, each fuel injector may be connected to asense injector line that shows the fuel injection activity for eachcylinder. The sense injector lines associated with cylinder group 210may be inputs into “AND” logic gate 902 and the sense injector linesassociated with cylinder group 212 may be inputs into “AND” logic gate904. The outputs of the “AND” logic gates 902 and 904 may providesignals showing whether or not there is fuel injector activity in eitherof the cylinder groups. The outputs of “AND” logic gates 902 and 904further may be inputs into exclusive “OR” logic gate 906, in order toprovide a feedback signal to electronic engine controller 12, which mayindicate whether or not there is injector activity only in a singlegroup of cylinders (i.e. fuel injector cut-out mode).

It should be appreciated that the above described Boolean logic circuitis exemplary. Note that the exemplary circuit may be included as part ofa larger logic circuit. Alternatively, other logic operations may beperformed to indicate fuel injector activity and detection of a fuelinjector cut-out mode from the sense injector lines. In someembodiments, the logic circuit may include feedback from a commandedfuel injection signal. Although the Boolean logic circuit isschematically illustrated with discrete logic gates, it should beappreciated that in some embodiments, logical operations may beperformed using customizable integrated circuits, a programmablemicrocontroller and/or the engine controller.

Referring to FIG. 10, a truth table 1000 and graphical representation1010 show the possible inputs (i.e. cylinder group specific fuelinjector activity) and outputs (i.e. fuel injector cut-out modedetermination) of the exclusive “OR” logic circuit. In a first exemplarycondition, for example such as during a key-on and engine-off situation,both inputs values may be zero. Accordingly, the circuit may produce anoutput value of zero indicating that a fuel injector cut-out mode isinactive.

In a second exemplary condition, for example such as when the engine isrunning with all cylinders active, both input values may be one.Accordingly, the circuit may produce an output value of zero indicatingthat a fuel injector cut-out mode is inactive.

In a third exemplary condition, for example during a fuel injectorcut-out mode a first input value may be one and a second input value maybe zero. Accordingly, the circuit may produce an output value of oneindicating that a fuel injector cut-out mode is active. Similarly, in aforth exemplary condition the engine may operate in fuel injectorcut-out mode with the other cylinder group disabled. Accordingly, theinput values of the circuit may be zero and one and the output value maybe one indicating that fuel injector cut-out mode may be active.

Note that fuel injector activity further may be represented according toa fuel injection pulse frequency. Additionally, in some embodiments fuelinjector activity/inactivity may be determined according to a timethreshold which may be longer than the fuel injector pulse frequency.Such that when elapsed time between fuel injection pulses remains belowthe threshold, the fuel injectors may be determined to be active.Furthermore, if time elapses longer than the threshold time, the fuelinjectors may be determined to be inactive.

Note that in some embodiment the routine may further detect cylindergroup sub-set fuel injector degradation. A group sub-set may include oneor more cylinders in a cylinder group. Furthermore, fuel injectoractivity sensors may be configured to detect the fuel injection activityof a particular cylinder group sub-set.

Continuing on with routine 800, if it is determined that the fuelinjector cut-out mode is active, the routine moves to 830. At 830, theactual fuel injector activity of each group or bank of fuel injectorsmay be compared to the desired fuel injector activity for each enginebank.

Next at 832, routine 800 determines if only the desired group of fuelinjectors is active. If only the desired group of fuel injectors isactive then a fault counter is decremented at 536. Otherwise, the faultcounter is incremented at 834. Next at 838, the fault counter iscompared to a calibratible threshold. The threshold may be calibrated tovary the tolerance of the control strategy to account for componentdegradation, desired engine output, or another suitable calibrationmetrics. If it is determined that the fault counter is greater than thecalibratible threshold then a sense injector activity condition flag isset, at 840. Otherwise, if it is determined that the fault counter isnot greater than the calibratible threshold then the routine ends. Note,that the setting of a condition flag may result in various operationalchanges that will be discussed in further detail below.

Referring back to 820, if it is determined that the fuel injectorcut-out mode is inactive, the routine moves to 850 and undergoes asimilar sub-routine to verify the fuel injector activity in both groupsof cylinders. Namely, at 850, the actual fuel injector activity in eachgroup of cylinders is compared to the commanded injector activity foreach group of cylinders. At 852, routine 800 determines if both groupsof cylinders show the same fuel injector activity (i.e. both groups areactive or inactive). If it is determined that the fuel injector activityis, in fact, the same between the groups of cylinders then the faultcounter is decremented at 856. If it is determined that the fuelinjector activity differs between the groups of cylinders the faultcounter is incremented at 854.

Next at 858, the fault counter is compared to a calibratible threshold.As discussed above, the threshold may be calibrated according to variousoperational conditions and control strategies. If it is determined thatthe fault counter is greater than the calibratible threshold then asense injector activity fault (or condition) flag is set, at 860.Otherwise, if it is determined that the fault (or condition) counter isnot greater than the calibratible threshold then the routine ends.Accordingly, fuel injector activity verification routine 800 may berepeated numerous times throughout engine operation in order to providea robust engine control strategy.

In this way fuel injector activity may be verified during differentmodes of engine operation to aid in reducing an undesired engineresponse upon an error in fuel injector cutout control.

Note, that the setting of a condition flag may result in various enginecontrol strategy reconfigurations included in the default mode strategy(discussed in further detail below with regard to FIG. 6).

In some embodiments, the fuel injector activity verification routine maybe used in combination with the maximum torque estimation routine asdiscussed above (see FIGS. 3A-3B). For example, an engine controlstrategy may include modes to improve fuel economy, such as fuelinjector cut-out mode. In such a strategy, air load may be increased byoperating cylinder valves without injecting fuel to maintain a desiredtorque. In such situations, it may be desirable to verify fuel injectoractivity in order to reduce torque produced when the air load isincreased. In this way, the fuel injector activity verification routinemay be used to make the maximum torque estimation more robust.

Note that the fuel injector activity verification routines as describedabove also may be applied to variable displacement engine controlstrategies where both fuel injection and cylinder valve operation may bedeactivated. In particular, fuel injection activity may be monitoredusing the above described routine to aid in reduce the likelihood ofhydro-locking the engine due to fuel injection activity in deactivatedcylinders.

One embodiment advantageously implements a high-level diagnostic routineas part of the default operation strategy. Specifically, the diagnosticroutine monitors performance conditions during various modes of engineoperation in order to determine if the engine is able to perform asdesired in the particular mode of operation. Furthermore, the diagnosticroutine may make degradation determinations regarding differentcomponents based on detection of various operating conditions. Forexample, a determined degradation may result in setting a service codein the electronic engine controller. Additionally, in some embodiments adegradation determination may result in the change of an engine,powertrain, and/or vehicle operating parameter. Moreover, thedegradation determination may result in prevention of entering orexiting specific operational modes, or may trigger mode transitions, inorder to accommodate driver demand.

Referring to FIG. 6, diagnostic routine 600 detects the mode of engineoperation at 610. In the illustrated embodiment, the determination mayresult in one of five monitored engine modes, including lean bum, DeSOx,lean bum fuel injector cut-out, stoichiometric fuel injector cut-out andstoichiometric operation. However, it should be appreciated that in someembodiments various modes of operation may be omitted or added to thelist of monitored engine modes in the diagnostic routine.

If it is determined that the engine is operating in lean bum mode, theroutine moves to 620 to begin the lean bum diagnostic sub-routine.

At 622, diagnostic routine 600 determines if a condition has occurredshowing degradation of the feedgas UEGO sensor. Note that degradation ofthe feedgas UEGO sensor may be detected when the associated engine bankis command to run lean due to the linear nature of the UEGO sensoroutput. If it determined that the feedgas UEGO sensor has degraded, theroutine move to 628.

Otherwise, diagnostic routine 600 determines if a condition has occurredbased on degraded validation of the air-fuel ratio between the feedgasUEGO sensor and the tailpipe UEGO sensor at 624. This condition may beretrieved from air-fuel validation routine 400 (discussed above). If itis determined that the air-fuel validation has degraded, it may beassumed that the tailpipe UEGO sensor has degraded and the routine movesto 628.

Otherwise, diagnostic routine 600 determines if a condition has occurredbased on degradation of components relating to the electronic throttlecontrol (ETC) and the torque monitor independent plausibility check(IPC) of the vehicle at 626. If it is determined that a componentdegradation condition has occurred the routine moves to 628. Otherwise,no degradation condition has been detected and the routine ends.

At 628, diagnostic routine 600 has detected degradation of a componentthat affects the performance of the engine, and further affects theeffectiveness of the engine control strategy. Specifically, lean bumdiagnostic sub-routine 620 may concentrate on detection of UEGO sensordegradation since the lean bum engine control strategy uses accuratedetection of the air-fuel ratio to adjust the engine output such thatboth engine banks or groups run lean. Accordingly, diagnostic routine600 may reconfigure the engine control strategy in order to avoid enginemode degradation and to facilitate driver demand. Specifically, theroutine may initiate a coordinated exit from lean bum engine mode.

If it is determined that the engine is operating in DeSOx mode, theroutine moves to 630 to begin the DeSOx diagnostic sub-routine.

At 632, diagnostic routine 600 determines if a condition has occurredshowing degradation of the feedgas LEGO sensor. Note that due to thelinear nature of the UEGO sensor output, degradation of the feedgas UEGOsensor may be detected when the associated engine bank is command to runlean. If it determined that the feedgas UEGO sensor has degraded, theroutine moves to 638.

Otherwise, diagnostic routine 600 determines if a condition has occurredbased on degraded validation of the air-fuel ratio between the feedgasUEGO sensor and the tailpipe UEGO sensor at 634. This condition may beretrieved from air-fuel validation routine 400 (discussed above). If itis determined that the air-fuel validation has degraded, it may beassumed that the tailpipe UEGO sensor has degraded and the routine movesto 638.

Otherwise, diagnostic routine 600 determines if a condition has occurredbased on degradation of components relating to the electronic throttlecontrol (ETC) and the torque monitor independent plausibility check(IPC) of the vehicle at 636. If it is determined that a componentdegradation condition has occurred the routine moves to 638. Otherwise,no degradation condition has been detected and the routine ends.

At 638, diagnostic routine 600 has detected degradation of a componentthat affects the performance of the engine, and further affects theeffectiveness of the engine control strategy. Specifically, DeSOxdiagnostic sub-routine 630 may concentrate on detection of UEGO sensordegradation since the DeSOx engine control strategy uses accuratedetection of the air-fuel ratio to adjust the engine output such thatone engine bank or group runs lean and the other engine bank or groupruns rich. Accordingly, diagnostic routine 600 may reconfigure theengine control strategy in order to avoid engine mode degradation and tofacilitate driver demand. Specifically, the routine may initiate acoordinated exit from DeSOx engine mode.

If it is determined that the engine is operating in lean bum fuelinjector cut-out mode, the routine moves to 640 to begin the lean burnfuel injector cut-out diagnostic sub-routine.

At 642, diagnostic routine 600 determines if a condition has occurredshowing degradation of the feedgas UEGO sensor. Note that due to thelinear nature of the UEGO sensor output, degradation of the feedgas UEGOsensor may be detected when the associated engine bank is command to runlean. Additionally, in some embodiments, this act may be omitted sincethe feedgas UEGO sensor may provide incomplete readings during lean buminjector cut-out mode due to some engine configurations (i.e. cylindergroupings). If it determined that the feedgas UEGO sensor has degraded,the routine moves to 638.

Otherwise, diagnostic routine 600 determines if a condition has occurredbased on unexpected fuel injector activity read off the sense injectorline at 634. This condition may be retrieved from fuel injector activityverification routine 500 (discussed above). If it is determined thatunexpected fuel injector activity has occurred more times than acalibratible threshold, it may be assumed that a fuel injection systemrelated component has degraded and the routine moves to 648.

Otherwise, diagnostic routine 600 determines if a condition has occurredbased on degradation of components relating to the electronic throttlecontrol (ETC) and the torque monitor independent plausibility check(IPC) of the vehicle at 646. If it is determined that a componentdegradation condition has occurred the routine moves to 648. Otherwise,no degradation condition has been detected and the routine ends.

At 648, diagnostic routine 600 has detected degradation of a componentthat affects the performance of the engine, and further affects theeffectiveness of the engine control strategy. Specifically, lean bumfuel injector cut-out diagnostic sub-routine 640 may concentrate ondetecting fuel injector degradation since the lean bum fuel injectorcut-out engine control strategy uses accurate detection of fuel injectoractivity to reduce increased torque production. Accordingly, diagnosticroutine 600 may reconfigure the engine control strategy in order toreduce engine mode degradation and to facilitate driver demand.Specifically, the routine may initiate a coordinated exit from lean bumfuel injector cut-out engine mode and transition to another mode ofengine operation.

If it is determined that the engine is operating in stoichiometric fuelinjector cut-out mode, the routine moves to 650 to begin thestoichiometric fuel injector cut-out diagnostic sub-routine.

At 652, diagnostic routine 600 determines if a condition has occurredbased on unexpected fuel injector activity read off the sense injectorline at 652. This condition may be retrieved from fuel injector activityverification routine 500 (discussed above). If it is determined thatunexpected fuel injector activity has occurred more times than acalibratible threshold, it may be assumed that a fuel injection systemrelated component has degraded and the routine moves to 656.

Otherwise, diagnostic routine 600 determines if a condition has occurredbased on degradation of components relating to the electronic throttlecontrol (ETC) and the torque monitor independent plausibility check(IPC) of the vehicle at 654. If it is determined that a componentdegradation condition has occurred the routine moves to 656. Otherwise,no degradation condition has been detected and the routine ends.

At 656, diagnostic routine 600 has detected degradation of a componentthat affects the performance of the engine, and further affects theeffectiveness of the engine control strategy. Specifically,stoichiometric fuel injector cut-out diagnostic sub-routine 650 isconcentrated on detecting fuel injector degradation since thestoichiometric fuel injector cut-out engine control strategy usesaccurate detection of fuel injector activity reduce torque production.Accordingly, diagnostic routine 600 may reconfigure the engine controlstrategy in order to reduce engine mode degradation and to facilitatedriver demand. Specifically, the routine may initiate a coordinated exitfrom stoichiometric fuel injector cut-out engine mode and transition toanother mode of engine operation.

In the above described routine, note that upon detection of componentdegradation, coordinated exit from an engine mode may be implemented aspart of the default operation strategy. In one embodiment, the strategymay prioritize maintaining engine output over component degradation upondetection of a degraded mode of engine operation. Specifically,immediate exit from a potentially degraded engine mode may be preventedin order to maintain engine output in accordance with driver demand fora specified transition duration. For example, the strategy may preventexit from lean bum engine mode when the air load has been raised inorder to maintain driver requested torque.

Coordinated exit from an engine mode may further include areconfiguration of the engine control strategy. In particular, thecontroller may prevent entry into a mode based on detection of adegradation condition. Furthermore, detection of a degradation conditionmay cause the controller to prevent entry into multiple modes of engineoperation. For example, if a UEGO sensor detecting air-fuel readings fora cylinder group is determined to be degraded, the engine controlstrategy may prevent entry into any modes where the cylinder groupoperates with a lean air-fuel ratio in order to reduce engine controlerrors.

Furthermore, in some embodiments the engine may transition out ofdifferent modes at different rates in order to accommodate changes inoperating conditions. For example, a transition out of stoichiometricengine operation mode to a lean burn fuel injector cut-out mode mayoccur faster than another mode transitions such as transitioning out ofa fuel injector cut-out mode. Specifically, once fuel injection isdisabled in a cylinder group, air load may need to be increased quicklyto increase engine torque output in order meet driver demands.

As another example, during a fuel injector cut-out mode, air load in theengine may be increased to produce a sufficient amount of torque in theactive cylinder group. If the engine transitions out of the fuelinjector cut-out mode to a mode where all cylinder groups combust airand fuel without allowing for the air in the engine to decrease andmatch the injected fuel, errors in torque output and emissions may beincreased. Therefore, the mode transition may last over a longerduration than the above mentioned transition out of stoichiometricengine operation.

Note that in some embodiments, an engine mode transition in response tosensor degradation may be slower than a mode transition in response to adriver request in order to provide a period to match air and fuelamounts as discussed above, thus reducing the likelihood of increasedemissions due to un-matched air and fuel amounts.

Furthermore, it should be appreciated that high level diagnostic routine600 may be repeated numerous times throughout engine operation in orderto provide a robust engine control strategy. Alternatively, in someembodiments the diagnostic routine may be omitted from the enginecontrol strategy.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1. A multi-cylinder group engine system operable in at least a firstmode and a second mode, wherein the first mode a first and secondcylinder group combust air and fuel, and wherein the second mode atleast one of the first and second cylinder groups combusts air and fueland the other one of the first and second cylinder groups pumps airwithout injected fuel, the engine system comprising: a first linearexhaust gas sensor disposed in a first exhaust passage to measureair-fuel exhausted from the first cylinder group; a second exhaust gassensor disposed in a second exhaust passage to measure air-fuelexhausted from the second cylinder group; a third linear exhaust gassensor disposed downstream of a junction between the first exhaustpassage and the second exhaust passage; and a controller configured tovalidate a reading of the first linear exhaust gas sensor during thefirst mode of engine operation based on a reading of the second exhaustgas sensor when a lean air-fuel ratio is commanded.
 2. The system ofclaim 1 wherein the controller is further configured to validate areading of the first linear exhaust gas sensor during the first mode ofengine operation based on a reading of the third linear exhaust gassensor when the first linear exhaust gas sensor and the second exhaustgas sensor detect a lean air-fuel ratio.
 3. The system of claim 1wherein the controller is further configured to disable validation of areading of the first linear exhaust gas sensor based on a reading of thethird linear exhaust gas sensor when the engine is operating in thesecond mode.
 4. The system of claim 1 wherein the controller is furtherconfigured to disable validation of a reading of the first linearexhaust gas sensor based on a reading of the third linear exhaust gassensor when at least one cylinder in at least one of the first andsecond cylinder groups is pumping air without injecting fuel.
 5. Thesystem of claim 1 wherein the controller is further configured todisable validation of a reading of the first linear exhaust gas sensorbased on a reading of the third linear exhaust gas sensor responsive todetection of a cylinder misfire over a predetermined duration.
 6. Thesystem of claim 1 wherein the controller is further configured to usethe air-fuel reading of the first linear exhaust sensor to control fuelinjection in both the first and the second cylinder groups during thefirst mode of engine operation.
 7. The system of claim 1 wherein thesecond exhaust gas sensor is a linear exhaust gas sensor.
 8. The systemof claim 1 wherein the second exhaust gas sensor is a switching typeexhaust gas sensor.
 9. The system of claim 1 wherein the controller isfurther configured to disable lean air-fuel operation in at least one ofthe first and second modes of engine operation based on unsuccessfulvalidation of first linear exhaust gas sensor reading.
 10. A systemcomprising: an engine including a first cylinder group and a secondcylinder group; an exhaust system coupled to the engine, wherein thefirst cylinder group exhausts gas into at least a first exhaust passageand the second cylinder group exhausts gas into at least a secondexhaust passage; a first linear exhaust gas sensor disposed in the firstexhaust passage; a first switching type exhaust gas sensor disposed inthe second exhaust passage; a second linear exhaust gas sensor disposeddownstream from a junction of the first exhaust passage and the secondexhaust passage; and a controller configured to operate the engine in afirst mode where the first and second cylinder groups combust air andfuel, and a second mode where at least one of the first and secondcylinder groups combusts air and fuel and the other one of the first andsecond cylinder groups pumps air without injecting fuel, and thecontroller is further configured to validate a reading of the firstlinear exhaust gas sensor based on a reading of the second linearexhaust gas sensor during the first mode of engine operation when a leanair-fuel ratio is commanded.
 11. The system of claim 10 wherein thecontroller is further configured to validate a reading of the firstlinear exhaust gas sensor based on a reading of the second linearexhaust gas sensor during the first mode of engine operation when thefirst linear exhaust gas sensor and the first switching type exhaust gassensor detect a lean air-fuel ratio.
 12. The system of claim 10 whereinthe controller is further configured to disable validation of a readingof the first linear exhaust gas sensor based on a reading of the secondlinear exhaust gas sensor when the engine is operating in the secondmode.
 13. The system of claim 10 wherein the controller is furtherconfigured to disable validation of the first exhaust gas sensor basedon a reading of the second exhaust gas sensor when at least one cylinderin at least one of the first and second cylinder groups is pumping airwithout injecting fuel.
 14. The system of claim 10 wherein thevalidation is based on a threshold operating range based on relativemaximum and minimum air-fuel values measured by the first linear exhaustgas sensor at the beginning of the validation sequence.
 15. The systemof claim 10 wherein the controller is further configured to trigger adiagnostic trouble code based on unsuccessful sensor validation.
 16. Thesystem of claim 10 wherein the controller is further configured toadjust engine torque based on an air-fuel reading of the first linearexhaust gas sensor only upon successful validation of the reading of thefirst linear exhaust gas sensor.
 17. A method for detecting exhaust gassensor degradation in an engine system, the engine having an asymmetricexhaust gas sensor configuration to provide air-fuel feedback forcontrol of engine output, the method comprising: measuring lean air-fuelratio readings over a first duration by a first linear exhaust gassensor; measuring lean air-fuel ratio readings over a second duration bya second linear exhaust gas sensor downstream from the first linearexhaust gas sensor based on detection of oxygen breakthrough in acatalyst; shifting the first measurement duration to correspond to thesecond measurement duration based on an exhaust gas transportationduration; comparing the air-fuel ratio readings of the first and secondsensors during the corresponding measurement durations; and setting adegradation condition responsive to a discrepancy between the readingsof the first and second sensors during the corresponding measurementdurations.
 18. The method of claim 17 wherein the air-fuel readings ofthe first sensor include an operating range based on relative maximumand minimum air-fuel ratios measured during the first duration.
 19. Themethod of claim 17 wherein the degradation condition includes preventingentry into a mode of lean engine operation.
 20. The method of claim 17wherein the comparison of the air-fuel reading is suspended until oxygenbreakthrough in a catalyst has been determined.